Automatic volume control



:EOD-1517 Examine Sept. 7, 1937. K, A. cHlTTlcK AUTOMATIC VOLUME CONTROL Filed Dec. 16, 1935 2 Sheets-Sheet l Egg/ l I@ H MW 0, (T

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' ATTORNEY Sept.. 7, 1937. K A CH1TT|CK 2,092,500

AUTOMATIC VOLUME CONTROL Filed Dec. 16, 1935 2 Sheets-Sheet 2 INVENTOR A TTORNEY Patented Sept. 7, 1937 UNTTED STATES 2,092,500 AUTOMATIC VOLUME CONTROL Kenneth A. Chittick, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 16, 1933, Serial No. 702,674

1 Claim.

My present invention relates to gain control arrangements for high frequency signalling systems, and more particularly to automatic volume control circuitsV for radio receivers.

One of the main objects of my present invention is to provide an automatic volume control arrangement for a radio receiver wherein a direct current potential variation in a positive cold electrode circuit of the intermediate frequency amplifier is employed for regulation of the gain of a preceding high frequency transmission network.

Another important object of the present invention may be stated to be the provision, in a superheterodyne receiver, of an automatic volume control network wherein direct current potential variations across a resistor in the screen grid circuit of the intermediatel frequency amplifier is utilized for automatic control of the gain of a preceding high frequency amplifier.

Another object of the present invention is to provide an automatic volume control system for a superheterodyne receiver, the system utilizing direct current potential variations produced acrossa resistor in a positive cold electrode cir- 0 cuit of the second detector for high frequency amplier gain regulation.

Still other objects of the present invention are to improve generally the simplicity and efficiency of automatic volume control circuits, and to particularly provide a receiver wherein automatic volume control bias is secured without the use of an auxiliary control tube and which automatic volume control is constructed and assembled in a radio receiver in an economical manner.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claim. The invention itself, however, both as to its organization and method of operation, will best be understood by reference to the accompanying drawings, wherein several circuit arrangements of thepresent invention are shown and described.

In the drawings:-

Fig. 1 diagrammatically shows one circuit arrangement embodying the present invention,

Fig. 2 shows a modified form ofthe invention, l

wherein like reference characters in the different figures designatesimilar circuitl elements,

,there is shown in Fig. 1 one embodiment of the invention, the embodiment comprising 'a super- (Cl. Z50-20)` heterodyne receiver of conventional construction.

The receiver, since conventional and well known to those skilled in the art, will only be briey described. It comprises one or more stages of radio frequency amplification I, these stages be-l ing uni-controlledly tunable in any well known manner. The input to the amplifier l includes the usual signal collecting circuit A, and, although shown as a grounded antenna system, is to be clearly understood as being capable of replacement by any other well known collector of signal energy.

The amplier network I is followed by a network 2 which isy designated 1st Det-Local Oscillator, but it is to be clearlyunderstood that this network may embody a separate local oscillator and a separate rst detector, or may be of the combined oscillator-detector type. In many cases, as where compactness is desired, the

network 2 may be a combined oscillator-detector A circuit of the type disclosed and claimed by J. C. Smith in application Serial No. 654,421, filed J anuary 31st, 1933. In the latter case the network l can be omitted, and the automatic volume control arrangement to be hereinafter described applied to the signal control electrode of the combined oscillator-detector. y

The intermediate frequency output of the network 2, regardless of how obtained, is impressed between the input electrodes of the intermediate frequency amplifier tube 3. The coupling between the network 2 and the input electrodes of tube 3 includes a pair of coupled resonant circuits 4, 5, both tuned to the operating intermediate frequency; and the tube 3 is of the pentode type and is well known to those skilled in the art. The amplified intermediate frequency energy istransmitted from the tube 3 to the succeeding second detector 6 through a coupling network which includes the coupled resonant circuits l, 8, the latter being tuned to the operating intermev diate frequency. The second detector output may be impressed upon an audio frequency arnplier and the amplified audio frequency energy reproduced in a reproducer of the electromagnetic or electrodynamic type.

The numerals 9 and l0 designate the positive and negative power supply leadsconnected between the power supply source, not shown, and the pertinent electrode circuits of the receiver. It is to be clearly understood that the power supply source may be the usual power supply lter succeeding the rectifier tube when used with an` alternating current supply, but the power supply source may also be a network adapted for use directly with a commercial direct current or alternating current supply. In any case, the negative lead II! includes in series therewith the reproducer field coil II, the eld coil being inserted in the lead IIJ in such a manner that its positive side is connected to ground, as at I2. In this way the reproducer eld coil is energized, and also provides a convenient means for seeming ay potential drop for other purposes. The connections from the positive lead 9 and bleeder 9 to the Various electrode circuits are not shown since those skilled in the art will readily understand how the bleeder'is tobe con-- nected to provide a completely connected circuit.

The signal control electrodeyof tube 3 isconnected to the negative side of the eld coil II through a path which includes the tuned circuit 5, the lead I3, the resistor I4, and thelead I5. The cathode of tube 3 is connected to the positive side of resistor I4 through a path which includes the lead`I6. The leadsfl'and IB-are connectedlthrougha, lter choke I'I, and the latter functions to smooth out hum ripple in the power supply. The choke Il: is shunted across the resistor I4, andthe cathode of tube 3 is shown connected to'thespositive,v side of choke I'I, while theleadzl5 is connected to the negative side of choke Il. l

The pointfon the resistor I4 to which the signal control electrode of tube-3 is connected is designated by the reference character P, and this point is represented as being negative in potential withtv respect to the point of resistor I4 to which the cathodeof tube 3 is connected. The screengrid electrode of tube 3 is connected to the lead. I0 through a path which includes lead I8 and resistor R,'whi1e the anode of tube 3 is connected to the lead IIJ by a path which includes'the tuned circuit 'I and the lead I9. The

resistorv R isl shunted by a radio frequency bytrolled amplifier, or to the different signal grids` passcondenser 20,' and a lead 2l conductively connects the negative side of resistor R to the gain control electrode of the'radio frequency ainplifier to be controlled. v

A dotted line 22 is shown between the symbol` in-network I representing-the controlgrid-and the lead 2|, and it will be clearly understood that this'dotted line designates the gain control connection to the signal control grid of thel conif morethan one controlled amplifier is used. The specilcgain control connections between rthe controlled ampliiier I and the leady 2I are not shown in detail because theyare well known to those skilled in the art and can readily be supplied, the lead 2| merely being designated .A; V. C. to clearly'show the function thereof.

It is believed that the operation of the arrangement shown in Fig. 1 will be clear from the aforegoing description, it being additionally pointed out that the intermediate frequency 'amplifier tube-3 vhas its signal control grid biased by con-v nection to point P to such `a value that the current flowing in the screen'resistor vRgenerates 5 just enough bias for the residual bias on the controlled amplifier network I; The anode current oftube 3 is also'reduced inv like manner. When a Vsignal is receivedthe eiective bias of the tube 3 is reduced,and allows more screen and anode current to iiow.` This eifect increases the automatic volume controll biasfor amplifier control, and also the'gain in the tube for intermediate frequency amplification.

The amount ,ofthe desired bias supplied by the position must be connected in close voltage proximity` with respect to the controlled amplifier tubes. in order to produce the current polarity for automatic volume control bias. 'Ihis anode and screen voltage may also be obtained from a suitable resistor orbleeder voltage not associated directly with` the lter supply system, provided the respective voltage relation of resistor R to the cathode of the Acontrolled amplier tubes is maintained..

The arrangement shown in Fig. 1 acts like a partial noise suppressor. asthe intermediate frequency gainin tube 3 is reduced when no signal is g received. This is so because in the tube arrangement shown the control gridhas more than normal. bias in orderto obtain the desired voltage drop in resistor R`whenrno signal is obtained.

When 'the signal voltage is impressed on the conv trol grid, the effective bias is reduced and the gain of the tube is increased.v Ofl course, the screen and anode of tube 3 may be reversed depending upon the characteristicsv ofthe tube.

That is to say, the control resistor R may be disfier stage may be obtained with any tube element q or combination of tube elements suitable for this purpose.

In Fig. 2-is shown a modication of the invention wherein the -construction and' functionsA show-n in Fig. 1 are embodied in the second detector circuit. The symbol 3' designates the seconddetector tube, which is-of thesame pentode type shown in yconnection with tube 3 in Fig.-1 the tuned intermediate frequency input circuit 8 being connected between the signal control electrode and the cathode through a negative potential source I4. The cathode is connected to point P' on vthe bleeder resistor 30, one side ofthe latter being connected to the negative terminal of the power supply source, an intermediate point on the bleeder being connected to ground. The screen electrode lead I8 is connected to a proper positive potential point vthrough a path which includes the radio frequency choke 3i and the primary winding 32 of the audio frequency transformer T, the transformer being arranged for connection to the usual audio frequency amplifier.

The anodey of tube 3 includes the automatic volume control circuit, and the lead I9 thereto includes the radio frequency` choke 33, the control Vresistor Ri being connected between one side of the choke 33 and ground. lI'he negative sideA in Fig. 1, the signal functioning on the bias of tube 3 in the same manner. The screen and anode circuits may be reversed as to function in tube 3', as stated in connection with tube 3 of Fig. 1. The various functions of automatic volume control voltage supply and detection may be obtained with any tube element or combination of tube elements suitable for this purpose.

',I'he operation of the arrangement in Fig. 2 is as follows: When signal Voltage is impressed on the control grid, the effective bias is reduced which increases the anode current for automatic volume control bias. The screen current flow also increases. This increase in screen current increases the detecting properties of the tube, and relieves the noise suppression feature.

In Fig. 3 is shown another modification of the invention in which the tube 56 includes two sections which perform different functions in one envelope. This tube is of the type known as 6F7, and comprises a pentode section and a triode section having a common cathode. The control grid 5l and the control grid 52 of the pentcde and triode sections respectively are connected together through a condenser 53. 'Ihe cathode of tube 50 is connected to point P1 on the divider resistor 5G; the control grid 5l is connected through lead 55 to point P2 on the divider for the normal grid bias; and the anode and screen of the pentode section of tube 50 are connected to proper positive potential points. The anode of the triode section of tube 50, which triode section functions to perform automatic volume control, is connected to ground through resistor R1 across which the automatic volume controll bias is developed. The control grid 52 of the automatic volume control section of tube 5D is connected to point P3 on divider 54 through lead 56 to obtain the proper negative grid bias.

The amount of this bias may be sufficient to provide current in resistor R1 for the residual grid bias for the amplifier tubes, or it can be of such a value that several volts of intermediate frequency voltage must be applied to the control grid before any automatic volume control bias is developed.

In operation, when signal is applied to both the control grids 5l and 52 in parallel the effective bias on the automatic volume control section of tube 50 is reduced as the signal is increased until current flows in resistor R1 and generates control voltage. This volume control bias is applied to the preceding radio frequency amplifier, or amplifiers, and may also be applied to the intermediate frequency amplifier 6D. When bias is applied to the tube 6D the amount of bias desired to make the overall amplifier fiat against signal voltage is obtained by tapping a portion of resistor R1 for this bias. This last named arrangement is disclosed in co-pending application Serial No. 642,544, filed November 14th, 1932, of Chittick and Carlson. I-Iere again the voltage supply may be obtained across a bleeder resistor and not across circuits shunting the rectifier filter system. In this modification the feature of noise suppression is not included. It is not necessary to explain the remaining portions of the circuit in detail, since they are either well known to those skilled in the art from their diagrammatic showing, or correspond to elements already described and explained in connection with Figs. 1 and 2.

In the modification shown in Fig. 4 there is shown an arrangement wherein the tube 60 is substituted for the tube 50 of Fig. 3. The tube 60 is of the type known as 2A?, and the various tube electrodes are supplied with proper operating voltages as shown in Fig. 4, and as illustrated in Fig. 3. Signal voltage is applied tov both control grids Gl and 62 connected in parallel through the coupling condenser 63. When the signal voltage increases, the effective bias on the automatic volume control grid electrode is reduced and current flows in resistor R2 thus generating volume control bias.

'I'his reduction in effective bias increases the anode current of the intermediate frequency amplifier section of tube 60 so that the tube also acts as a noise suppressor circuit. The additional intermediate frequency amplier tube 60 may be included between the second detector and tube 60 as shown in Fig. 3. No further description of Fig. 4 is believed necessary in view of the fact that it functions in a manner similar to Fig. 3, with the exception of the noise suppressor function.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claim.

What I claim is:-

In combination with a network including a tube whose gain is to be automatically controlled in accordance with variations 'in amplitude of received signal energy, a control network including a tube having its input electrodes coupled to the output of said first tube, a power supply source including an impedance connected between the cathode of said control tube and a positive electrode of the latter, the cathode being connected to a point on said impedance to which the positive electrode is connected, means connected between said impedance and the signal control electrode of said control tube for maintaining the said signal electrode sufficiently negative with respect to said cathode in the absence of signal amplitudes below a desired level to maintain a minimum current flow through the circuit of said positive electrode, a control resistor connected in series between said impedance and the positive electrode of said control tube for developing from said minimum current flow the sole operating bias for the controlled .tube which results in maximum Sensitivity of the latter, a second positive electrode within said control tube, a signal output circuit connected to said second positive electrode, and a conductive connection between a point of negative potential on said control resistor and a gain control electrode of said first tube.

KENNETH A. CHITTICK. 

